I. Field of the Invention
The present invention relates generally to applying torque to a fastener and, more particularly, to the measured tightening of a fastener in medical applications.
II. Discussion of the Prior Art
The use of surgical fixation systems involving screws is an accepted practice for a variety of orthopedic procedures. One procedure experiencing proliferated growth is that of spinal fixation, wherein surgical screws are bored into adjacent vertebral bodies and used to anchor rods to immobilize one or more spinal levels. Each screw generally comprises a shank for introduction into bone (such as a pedicle) and a housing or “tulip” coupled to the shank, either fixedly to form a “fixed axis screw” or adjustably to form a “multi-axis screw”. In either event, the rod is received within the housing of the screw and a fastener is employed to secure the rod within or to the housing. One manner of tightening the fastener within or to the housing involves the use of a basic torque driver, such as a screwdriver dimensioned to drive the fastener into engagement with the screw housing.
Although generally effective, this basic torque driver is nonetheless disadvantageous in that a surgeon must apply the entire torque necessary to properly tighten the fastener. Another drawback of the existing systems is that, to the extent such basic torque drivers include meters or “read outs,” such meters are challenging to read during the application of torque by the surgeon.
The present invention is directed at overcoming, or at least improving upon, the disadvantages of the prior art.